The blog entry “Glowing Roads?” makes some very good points about using light-transmitting concrete to illuminate roadways, sidewalks, etc. While this material has some obvious advantages for the future, it also has a couple of major drawbacks for near-term implementation. First, many roads are currently made out of asphalt because it is considerably cheaper than concrete. Replacing these roads with concrete roads would be expensive and replacing them with light-transmitting concrete roads would be even more expensive. The second drawback, also economic in nature, is the cost of the light sources (LEDs or whatever else might be used) as well as the cost of the energy to operate them.
Phosphorescent, or “glow-in-the-dark,” concrete is a material which is much more economically and technically feasible for the near future. A phosphorescent material is one which absorbs and stores energy when exposed to light and then releases that energy as a glowing light. This is a passive technology and does not require the input of any energy except for being exposed to a light source. For roads, of course, that light source would be the sun – free and abundant. A company named Glow, Inc. sells phosphorent pigment which can be added to concrete. Concrete treated with this pigment is currently being used for warehouse floors and emergency exit lighting. Concrete with this pigment in it glows green. It seems like this would be a very good (i.e., non-distracting) color for roads and/or road markings. It is not unreasonable to speculate that such a pigment could be used, or adapted for use, in asphalt also.
While light-transmitting concrete may well be used in the roads of the (more distant) future, phosphorescent concrete (and perhaps even phosphorescent asphalt) provide a solution which could be implemented in the very near future. Furthermore, if phosphorescent materials prove successful and/or if the economic drawbacks of light-transmitting concrete cannot easily be solved, then the phosphorescent materials might even be the long-tern solution.